Flexible vascular occluding device

ABSTRACT

A vascular occluding device for modifying blood flow in a vessel, while maintaining blood flow to the surrounding tissue. The occluding device includes a flexible, easily compressible and bendable occluding device that is particularly suited for treating aneurysms in the brain. The neurovascular occluding device can be deployed using a micro-catheter. The occluding device can be formed by braiding wires in a helical fashion and can have varying lattice densities along the length of the occluding device. The occluding device could also have different lattice densities for surfaces on the same radial plane.

RELATED APPLICATION

This application is a Continuation-in-part of and claims priority toU.S. application Ser. No. 11/136,395, filed May 25, 2005, which claimsthe benefit of U.S. Provisional Application Ser. No. 60/574,429,entitled “Flexible Vascular Prosthesis,” filed May 25, 2004. Each ofthese applications is expressly incorporated herein by reference intheir entireties.

FIELD OF THE INVENTION

The invention relates generally to an implantable device that could beused in the vasculature to treat common vascular malformations. Moreparticularly, it relates to a flexible, biocompatible device that can beintroduced into the vasculature of a patient to embolize and occludeaneurysms, particularly cerebral aneurysms.

BACKGROUND OF THE INVENTION

Walls of the vasculature, particularly arterial walls, may developpathological dilatation called an aneurysm. Aneurysms are commonlyobserved as a ballooning-out of the wall of an artery. This is a resultof the vessel wall being weakened by disease, injury or a congenitalabnormality. Aneurysms have thin, weak walls and have a tendency torupture and are often caused or made worse by high blood pressure.Aneurysms could be found in different parts of the body; the most commonbeing abdominal aortic aneurysms (AAA) and the brain or cerebralaneurysms. The mere presence of an aneurysm is not alwayslife-threatening, but they can have serious heath consequences such as astroke if one should rupture in the brain. Additionally, as is known, aruptured aneurysm can also result in death.

The most common type of cerebral aneurysm is called a saccular aneurysm,which is commonly found at the bifurcation of a vessel. The locus ofbifurcation, the bottom of the V in the Y, could be weakened byhemodynamic forces of the blood flow. On a histological level, aneurysmsare caused by damage to cells in the arterial wall. Damage is believedto be caused by shear stresses due to blood flow. Shear stress generatesheat that breaks down the cells. Such hemodynamic stresses at the vesselwall, possibly in conjunction with intrinsic abnormalities of the vesselwall, have been considered to be the underlying cause for the origin,growth and rupture of these saccular aneurysms of the cerebral arteries(Lieber and Gounis, The Physics of Endoluminal stenting in the Treatmentof Cerebrovascular Aneurysms, Neurol Res 2002: 24: S32-S42). Inhistological studies, damaged intimal cells are elongated compared toround healthy cells. Shear stress can vary greatly at different phasesof the cardiac cycle, locations in the arterial wall and among differentindividuals as a function of geometry of the artery and the viscosity,density and velocity of the blood. Once an aneurysm is formed,fluctuations in blood flow within the aneurysm are of criticalimportance because they can induce vibrations of the aneurysm wall thatcontribute to progression and eventual rupture. For a more detaileddescription of the above concepts see, for example, Steiger,Pathophysiology of Development and Rupture of Cerebral Aneurysms, ActaNeurochir Suppl 1990: 48: 1-57; Fergueson, Physical Factors in theInitiation, Growth and Rupture of Human Intracranial Saccular Aneurysms,J Neurosurg 1972: 37: 666-677.

Aneurysms are generally treated by excluding the weakened part of thevessel from the arterial circulation. For treating a cerebral aneurysm,such reinforcement is done in many ways: (i) surgical clipping, where ametal clip is secured around the base of the aneurysm; (ii) packing theaneurysm with microcoils, which are small, flexible wire coils; (iii)using embolic materials to “fill” an aneurysm; (iv) using detachableballoons or coils to occlude the parent vessel that supplies theaneurysm; and (v) endovascular stenting. For a general discussion andreview of these different methods see Qureshi, Endovascular Treatment ofCerebrovascular Diseases and Intracranial Neoplasms, Lancet. 2004 Mar.6;363 (9411):804-13; Brilstra et al. Treatment of Intracranial Aneurysmsby Embolization with Coils: A Systematic Review, Stroke 1999; 30:470-476.

As minimally invasive interventional techniques gain more prominence,micro-catheter based approaches for treating neurovascular aneurysms arebecoming more prevalent. Micro-catheters, whether flow-directed orwire-directed, are used for dispensing embolic materials, microcoils orother structures (e.g., stents) for embolization of the aneurysm. Amicrocoil can be passed through a micro-catheter and deployed in ananeurysm using mechanical or chemical detachment mechanisms, or bedeployed into the parent vessel to permanently occlude it and thus blockflow into the aneurysm. Alternatively, a stent could be tracked throughthe neurovasculature to the desired location. Article by Pereira,History of Endovascular Aneurysms Occlusion in Management of CerebralAneurysms; Eds: Le Roux et al., 2004, pp: 11-26 provides an excellentbackground on the history of aneurysm detection and treatmentalternatives.

As noted in many of the articles mentioned above, and based on theorigin, formation and rupture of the cerebral aneurysm, it is obviousthat the goal of aneurysmal therapy is to reduce the risk of rupture ofthe aneurysm and thus the consequences of sub-arachnoid hemorrhage. Itshould also be noted that while preventing blood from flowing into theaneurysm is highly desirable, so that the weakened wall of the aneurysmdoesn't rupture, it may also be vital that blood flow to the surroundingstructures is not limited by the method used to obstruct blood flow tothe aneurysm. Conventional stents developed for treating other vascularabnormalities in the body are ill suited for embolizing cerebralaneurysms. This could lead to all the usual complications when highoxygen consumers, such as brain tissue, are deprived of the needed bloodflow.

There are many shortcomings with the existing approaches for treatingneurovascular aneurysms. The vessels of the neurovasculature are themost tortuous in the body; certainly more tortuous than the vessels ofthe coronary circulation. Hence, it is a challenge for the surgeon tonavigate the neurovasculature using stiff coronary stents that aresometimes used in the neurovasculature for treating aneurysms. Thebending force of a prosthesis indicates the maneuverability of theprosthesis through the vasculature; a lower bending force would implythat the prosthesis is more easily navigated through the vasculaturecompared to one with a higher bending force. Bending force for a typicalcoronary stent is 0.05 lb-in (force to bend 0.5 inches cantilever to 90degree). Hence, it will be useful to have neural prosthesis that is moreflexible than existing stents.

Existing stent structures, whether used in coronary vessels or in theneurovasculature (microcoils) are usually straight, often laser cut froma straight tubing or braiding with stiff metallic materials. However,most of the blood vessels are curved. Hence, current stent structuresand microcoils impart significant stress on the vessel walls as they tryto straighten a curved vessel wall. For a weakened vessel wall,particularly where there is a propensity for an aneurysm formation, thiscould have disastrous consequences.

As noted earlier, the hemodynamic stress placed on the blood vessels,particularly at the point of bifurcation, leads to weakening of thevessel walls. The most significant source of such stress is the suddenchange in direction of the blood flow. Hence, if one were to minimizethe sudden change in direction of blood flow, particularly at thelocation of vessel weakness, it would be beneficial.

Existing approaches to occluding aneurysms could lead to another set ofproblems. Methods that merely occlude the aneurysm by packing or fillingit with embolic material (coils or liquid polymers) do not address thefundamental flow abnormalities that contribute to the formation ofaneurysm.

A stent structure could be expanded after being placed intraluminally ona balloon catheter. Alternatively, self-expanding stems could beinserted in a compressed state and expanded upon deployment. For balloonexpandable stents, the stent is mounted on a balloon at the distal endof a catheter, the catheter is advanced to the desired location and theballoon is inflated to expand the stent into a permanent expandedcondition. The balloon is then deflated and the catheter withdrawnleaving the expanded stent to maintain vessel patency. Because of thepotentially lethal consequences of dissecting or rupturing anintracerebral vessel, the use of balloon expandable stents in the brainis fraught with problems. Proper deployment of a balloon expandablestent requires slight over expanding of the balloon mounted stent toembed the stent in the vessel wall and the margin of error is small.Balloon expandable stents are also poorly suited to adapt to the naturaltapering of cerebral vessels which taper proximally to distally. If astent is placed from a parent vessel into a smaller branch vessel thechange in diameter between the vessels makes it difficult to safelydeploy a balloon expandable stent. A self-expanding stent, where thecompressed or collapsed stent is held by an outer restraining sheathover the compressed stent to maintain the compressed state untildeployment. At the time of deployment, the restraining outer sheath isretracted to uncover the compressed stent, which then expands to keepthe vessel open. Additionally, the catheters employed for deliveringsuch prosthesis are micro-catheters with outer diameter of 0.65 mm to1.3 mm compared to the larger catheters that are used for delivering thelarge coronary stents to the coronaries.

U.S. Pat. No. 6,669,719 (Wallace et al.) describes a stent and a stentcatheter for intra-cranial use. A rolled sheet stent is releasablymounted on the distal tip of a catheter. Upon the rolled sheet beingpositioned at the aneurysm, the stent is released. This results inimmediate and complete isolation of an aneurysm and surrounding sidebranches of the circulatory system and redirecting blood flow away fromthe aneurysm. A significant drawback of such a system is that thesurrounding side branches, along with the target aneurysm, are deprivedof the needed blood flow after the stent has been deployed.

U.S. Pat. No. 6,605,110 (Harrison) describes a self-expanding stent fordelivery through a tortuous anatomy or for conforming the stent to acurved vessel. This patent describes a stent structure with radiallyexpandable cylindrical elements arranged in parallel to each other andinterspersed between these elements and connecting two adjacentcylindrical elements are struts that are bendable. While this structurecould provide the necessary flexibility and bendability of the stent forcertain applications, it is expensive and complex to manufacture.

U.S. Pat. No. 6,572,646 (Boylan) discloses a stent made up of asuper-elastic alloy, such as Ni—Ti alloy (Nitinol), with a lowtemperature phase that induces a first shape to the stent and a hightemperature phase that induces a second shape to the stent with a bendalong the length. U.S. Pat. No. 6,689,162 (Thompson) discloses a braidedprosthesis that uses strands of metal, for providing strength, andcompliant textile strands. U.S. Pat. No. 6,656,218 (Denardo et al.)describes an intravascular flow modifier that allows microcoilintroduction.

SUMMARY OF THE INVENTION

An aspect of the present invention provides a highly flexibleimplantable occluding device that can easily navigate the tortuousvessels of the neurovasculature. Additionally, occluding device caneasily conform to the shape of the tortuous vessels of the vasculature.Furthermore, the occluding device can direct the blood flow within avessel away from an aneurysm; additionally such an occluding deviceallows adequate blood flow to be provided to adjacent structures suchthat those structures, whether they are branch vessels or oxygendemanding tissues, are not deprived of the necessary blood flow.

The occluding device is also capable of altering blood flow to theaneurysm, yet maintaining the desired blood flow to the surroundingtissue and within the vessel. In this instance, some blood is stillallowed to reach the aneurysm, but not enough to create a laminar flowwithin the aneurysm that would cause injury to its thinned walls.Instead, the flow would be intermittent, thereby providing sufficienttime for blood clotting or filler material curing within the aneurysm.

The occluding device is flexible enough to closely approximate thenative vasculature and conform to the natural tortuous path of thenative blood vessels. One of the significant attributes of the occludingdevice according to the present invention is its ability to flex andbend, thereby assuming the shape of a vasculature within the brain.These characteristics are for a neurovascular occluding device thancompared to a coronary stent, as the vasculature in the brain is smallerand more tortuous.

In general terms, aspects of the present invention relate to methods anddevices for treating aneurysms. In particular, a method of treating ananeurysm with a neck comprises deploying a vascular occluding device inthe lumen of a vessel at the location of the aneurysm, whereby the bloodflow is redirected away from the neck of the aneurysm. The inducedstagnation of the blood in the lumen of the aneurysm would createembolization in the aneurysm. The occluding device spans the width ofthe stem of the aneurysm such that it obstructs or minimizes the bloodflow to the aneurysm. The occluding device is very flexible in both itsmaterial and its arrangement. As a result, the occluding device can beeasily navigated through the tortuous blood vessels, particularly thosein the brain. Because the occluding device is flexible, very littleforce is required to deflect the occluding device to navigate throughthe vessels of the neurovasculature, which is of significance to theoperating surgeon.

A feature of the occluding device, apart from its flexibility, is thatthe occluding device may have an asymmetrical braid pattern with ahigher concentration of braid strands or a different size of braidstrands on the surface facing the neck of the aneurysm compared to thesurface radially opposite to it. In one embodiment, the surface facingthe aneurysm is almost impermeable and the diametrically opposed surfaceis highly permeable. Such a construction would direct blood flow awayfrom the aneurysm, but maintain blood flow to the side branches of themain vessel in which the occluding device is deployed.

In another embodiment, the occluding device has an asymmetrical braidcount along the longitudinal axis of the occluding device. This providesthe occluding device with a natural tendency to curve, and hence conformto the curved blood vessel. This reduces the stress exerted by theoccluding device on the vessel wall and thereby minimizing the chancesof aneurysm rupture. Additionally, because the occluding device isnaturally curved, this eliminates the need for the tip of themicro-catheter to be curved. Now, when the curved occluding device isloaded on to the tip of the micro-catheter, the tip takes the curvedshape of the occluding device. The occluding device could be pre-mountedinside the micro-catheter and can be delivered using a plunger, whichwill push the occluding device out of the micro-catheter when desired.The occluding device could be placed inside the micro-catheter in acompressed state. Upon exiting the micro-catheter, it could expand tothe size of the available lumen and maintain patency of the lumen andallow blood flow through the lumen. The occluding device could have alattice structure and the size of the openings in the lattice could varyalong the length of the occluding device. The size of the latticeopenings can be controlled by the braid count used to construct thelattice.

According to one aspect of the invention, the occluding device can beused to remodel an aneurysm within the vessel by, for example, neckreconstruction or balloon remodeling. The occluding device can be usedto form a barrier that retains occlusion material within the aneurysm sothat introduced material will not escape from within the aneurysm due tothe lattice density of the occluding device in the area of the aneurysm.

In another aspect of the invention, a device for occluding an aneurysmis disclosed. The device is a tubular with a plurality of perforationsdistributed on the wall of the member. The device is placed at the baseof the aneurysm covering the neck of the aneurysm such that the normalflow to the body of the aneurysm is disrupted and thereby generatingthrombus and ultimately occlusion of the aneurysm.

In yet another aspect of this invention, the device is a braided tubularmember. The braided strands are ribbons with rectangular cross section,wires with a circular cross section or polymeric strands.

In another embodiment, a device with a braided structure is made inorder to conform to a curved vessel in the body, where the density ofthe braid provides enough rigidity and radial strength. Additionally,the device can be compressed using a force less than 10 grams. Thisenables the device to be compliant with the artery as the arterial wallis pulsating. Also, the device is capable of bending upon applying aforce of less than 5 gram/cm.

Other aspects of the invention include methods corresponding to thedevices and systems described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention has other advantages and features which will be morereadily apparent from the following detailed description of theinvention and the appended claims, when taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is an illustration of an aneurysm, branch vessels and blood flowto the aneurysm.

FIGS. 2A and 2B illustrate one embodiment of an occluding device totreat aneurysms.

FIG. 3 is an illustration of the embodiment shown in FIG. 2 in acompressed state inside a micro-catheter.

FIG. 4A is another embodiment of an occluding device for treatinganeurysms.

FIGS. 4B and 4C illustrate cross sections of portions of ribbons thatcan be used to form the occluding device of FIG. 4A.

FIG. 5 shows the occluding device in a compressed state inside amicro-catheter being advanced out of the micro-catheter using a plunger.

FIG. 6 shows the compressed occluding device shown in FIG. 5 deployedoutside the micro-catheter and is in an expanded state.

FIG. 7 shows the deployed occluding device inside the lumen of a vesselspanning the neck of the aneurysm, a bifurcation and branch vessels.

FIG. 8 is a schematic showing the occluding device located in the lumenof a vessel and the change in the direction of the blood flow.

FIG. 9 shows the effect of a bending force on a conventional stentcompared to the occluding device of the present invention.

FIG. 10 demonstrates the flexibility of the current invention, comparedto a traditional stent, by the extent of the deformation for an appliedforce.

FIG. 11 shows the non-uniform density of the braid that provides thedesired curved occluding device.

FIG. 12 illustrates the difference in lattice density or porosity due tothe non-uniform density of the braiding of the occluding device.

FIG. 13 shows the varying lattice density occluding device covering theneck of an aneurysm.

FIGS. 14 and 15 show an embodiment of the vascular occluding devicewhere the lattice density is asymmetrical about the longitudinal axisnear the aneurysm neck.

FIG. 16 illustrates a bifurcated occluding device according to anembodiment of the present invention in which two occluding devices oflesser densities are combined to form a single bifurcated device.

FIG. 17 illustrates an example of a mesh pattern of a lattice in anoccluding device.

FIG. 18 illustrates an example of a braiding element of a lattice in anoccluding device.

FIG. 19 illustrates an example of another braiding element of a latticein an occluding device.

FIG. 20 illustrates a braiding element of an occluding device fittedinto a vessel diameter.

FIG. 21 is a cross sectional view of an example of a protective coil.

FIG. 22 illustrates an example of determining ribbon dimensions of anoccluding device in a protective coil or a delivery device.

FIG. 23 illustrates another example of determining ribbon dimensions ofan occluding device in a protective coil or a delivery device.

FIG. 24 illustrates an example of determining a ribbon width based on anumber of ribbons.

FIG. 25 illustrates a relationship between the PPI of the occludingdevice in a vessel versus the PPI of the occluding device in afree-standing state.

FIG. 26 illustrates an example of a maximum ribbon size that fits in aprotective coil.

FIG. 27 is a graph showing the opening sizes of braiding elements in theoccluding device as a function of the PPI of the lattice structure.

FIG. 28 illustrates the in-vessel PPI as a function of the braided PPIof a 32 ribbon occluding device

FIG. 29 illustrates the percent coverage as a function of the braidedPPI for a 32 ribbon occluding device.

FIG. 30 illustrates the opening sizes of braiding elements in theoccluding device as a function of the braided PPI of the latticestructure for a 32 ribbon occluding device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The devices shown in the accompanying drawings are intended for treatinganeurysms. They are generally deployed, using micro-catheters, at thelocation of a cerebral aneurysm that is intended to be treated. One suchsystem is disclosed in copending U.S. patent application titled “Systemand Method for Delivering and Deploying an Occluding Device Within aVessel”, U.S. Ser. No. 11/136,398 filed on May 25, 2005, which isincorporated herein by reference in its entirety. The embodiments of theendovascular occluding device according to aspects of the presentinvention is useful for treating cerebral aneurysms that are commonlytreated using surgical clips, microcoils or other embolic devices.

FIG. 1 illustrates a typical cerebral aneurysm 10 in the brain. A neck11 of the aneurysm 10 can typically define an opening of between about 2to 25 mm. As is understood, the neck 11 connects the vessel 13 to thelumen 12 of the aneurysm 10. As can be seen in FIG. 1, the blood flow 1within the vessel 13 is channeled through the lumen 12 and into theaneurysm. In response to the constant blood flow into the aneurysm, thewall 14 of lumen 12 continues to distend and presents a significant riskof rupturing. When the blood within the aneurysm 10 causes pressureagainst the wall 14 that exceeds the wall strength, the aneurysmruptures. The present invention could prevent such ruptures. Also shownin FIG. 1 are the bifurcation 15 and the side branches 16.

FIG. 2 illustrates one embodiment of a vascular occluding device 20 inaccordance with an aspect of the present invention. In the illustratedembodiment, the occluding device 20 has a substantially tubularstructure 22 defined by an outer surface 21, an inner surface 24 and athin wall that extends between the surfaces 21, 24. A plurality ofopenings 23 extend between the surfaces 21, 24 and allow for fluid flowfrom the interior of the occluding device 20 to the wall of the vessel.Occluding device 20 is radially compressible and longitudinallyadjustable.

FIG. 3 shows a micro-catheter 25 and the occluding device 20 inside themicro-catheter 25 in a compressed state prior to being released withinthe vasculature of the patient.

FIG. 4 illustrates another embodiment of the occluding device 30 havingtwo or more strands of material(s) 31, 32 wound in a helical fashion.The braiding of such material in this fashion results in a latticestructure 33. As can be understood, the dimension of the lattice 33 andthe formed interstices 34 is determined, at least in part, by thethickness of the strand materials, the number of strands and the numberof helices per unit length of the occluding device 30. For example, theinterstices 34 and/or the dimension of the lattice 33 may be determinedby the number of strands of material(s) 31, 32 wound in helical fashion.In one example, any number of braiding ribbons up to 16 braiding ribbonsmay be used (e.g., 5, 8, 10, 13, 15 or 16 braiding ribbons). In anotherexample, 16-32 braiding ribbons may be used (e.g., 20, 23, 25, 27, 30,or 32 braiding ribbons). In another example greater than 32 braidingribbons may be used such as, for example, 35, 40, 48, 50, 55, 60, 80,100, or greater braiding ribbons. Nevertheless, other values arepossible.

Hence, strands of material, such as ribbons, may intersect to form abraid pattern. The intersection of the strand material may be formed ineither a radial or axial direction on a surface of a forming device suchas a braiding mandrel. When the intersection of the strand material isalong an axial path, for example, the intersecting material may be at afixed or variable frequency. As one example of strand materialintersecting at a fixed frequency, the intersecting strand material maybe along any 1.0 inch axial path on the surface of the forming device(e.g., a braiding mandrel) to indicate the pick count. When theintersection of the strand material is along a radial path orcircumferential path, the spacing of the strand material may beuniformly or variably distributed. In one example of the strand materialalong a radial or circumferential path in which the spacing is uniformlydistributed, the spacing along the radial direction may be determinedbased on the following formula:(π)*(forming device diameter)/(# ribbons/2)  Eq. (1):

FIG. 18 illustrates an example of braiding elements or cells in theradial and PPI (picks per inch) directions. Any single element of thebraid (i.e., braid element) may be combined to form a mesh pattern asillustrated in FIG. 17 on a surface of a forming device (e.g., braidingmandrel). The braid is capable of impeding or disrupting the flow offluid (e.g., blood) in a vessel (e.g., blood vessel). The braid orlattice pattern, density, shape, etc. when the occluding device isdeployed in the vessel, may at least partially determine the flow withinthe vessel. Each of the parameters of the braid or lattice may also becontrolled by a user to control flow.

Parameters for determining the flow through an occluding devicecontaining a lattice pattern, density, shape, etc. include surfacecoverage of the occluding device and cell size of the braid or latticepattern. Each of these parameters may further characterize the geometryof the braid or lattice. Surface coverage may be determined as (surfacearea)/(total surface area), where the surface area is the surface areaof the frame or solid element and the total surface area is of theentire element (i.e., frame and opening).

Cell size may be determined as the maximum length defining a cellopening. Braiding patterns that increase surface coverage whiledecreasing cell size may have an increased effect on disrupting orimpeding the flow through the braid or lattice. Each of the parametersof surface coverage and cell size may further be enhanced by varying thewidth of the strand material (e.g., the ribbons), increasing the numberof strands of strand material defining the braid, and/or increasing thePPI (i.e., Picks Per Inch).

The braiding or lattice pattern as described may be further defined byvarious parameters including, for example, the number of strands (e.g.,ribbons), the width of each ribbon/strand, the braiding PPI, and/or thediameter of the forming device (e.g., mandrel diameter), to name a few.Based on the lattice parameters, a leg length and a ribbon angle may bedetermined. The leg length may define the length of an aspect of thebraiding element. For example, if the braiding element is diamond shapedas illustrated in FIG. 17, the length of one side of the diamond shapedbraiding element is the “leg length.” A ribbon angle may define theangle created by two intersecting aspects of the braiding element. Inthe example illustrated in FIG. 17, the ribbon angle is the angle formedbetween two adjacent sides of the diamond shaped braiding element.Radial spacing of braid elements in a lattice pattern can define thewidth of a braiding element in radial direction. FIG. 18 illustrates anexample of a radial spacing, leg length and ribbon angle of a braidelement.

Radial spacing of the lattice may be determined as set forth in Equation1 as follows:Radial Spacing (π)*(forming device diameter)/(# ribbons/2)  Eq. (1):

The braiding element may be fitted into a vessel based on the radialspacing or the diameter of the vessel. The radial spacing of the latticemay be adjusted based on the diameter of the vessel. For example, if thediameter of the vessel is small, the radial spacing may be adjusted to asmaller dimension while the leg length of the braid elements may bemaintained. Also in this example, the ribbon angle may also be adjustedto achieve the adjusted radial spacing. Adjusting the ribbon angle mayalso alter the spacing of the braid element in the PPI direction.

FIG. 19 illustrates an example of determining a radial spacing andribbon angle of a lattice structure in an occluding device. In thisexample, a lattice or braid contains sixteen interlacing ribbons, witheach ribbon being 0.004 inches wide and braided on a forming device suchas a mandrel with a diameter of 4.25 mm and 65 PPI. Thus, in thisexample, the number of braiding elements is sixteen, the ribbon width is0.004 inches, the spacing in the PPI direction is 1/65=0.01538 inchesand the diameter of the forming device (e.g., mandrel diameter) is 4.25mm. Hence, the radial spacing may be calculated as: Radialspacing=(π)*(forming device diameter)/(#ribbons/2)=(3.14)*(0.425/2.54)/(16/2)=0.0657 inches. FIG. 19 illustratesan example of a braiding element with a radial spacing of 0.0657 inches.In addition, the leg length of the example is 0.0337 inches, the ribbonangle is 153.65 degrees, and the spacing of the braiding element in thePPI direction, based on the ribbon angle and leg length is 0.0154inches.

FIG. 20 illustrates the example of FIG. 19 after the braiding element isfitted into an appropriate vessel diameter. In this example, the radialspacing is adjusted to a smaller length to accommodate a smaller vesseldiameter. The leg length remains constant at 0.0337 inches so the ribbonangle changes based on changes in the radial spacing. In this example,the radial spacing is adjusted to 0.06184 inches and the ribbon angle isadjusted to 132.79 degrees. Also, the spacing of the braid element inthe PPI direction is also changed. In this example, the spacing of thebraid element in the PPI direction increases from 0.0154 inches to0.0270 inches.

Table 1 illustrates additional examples of lattice or braid patterns ofvarying PPI, ribbon width (RW), or number of ribbons. In addition, eachof the braid patterns in Table 1 may produce patterns with the samepercent coverage within a vessel. TABLE 1 # ribbons 16 32 64 Braiddiameter (mm) 4.25 4.25 4.25 Braid diameter (in) 0.16732 0.16732 0.16732PPI 65.00 130.00 260.00 RW (mils) 4.0000 2.0000 1.0000 Node Spacing(ppi) 0.01538 0.00769 0.00385 Node Spacing (radial) 0.06571 0.032850.01643 Ribbon Angle (ppi) 153.65 153.65 153.62 Leg Length (in) 0.033740.01687 0.00844 Vessel diameter (mm) 4 4 4 In-vessel device Node spacing0.06184 0.03092 0.01546 In-vessel device Ribbon Angle (ppi) 132.79132.79 132.70 In-vessel device Node spacing 0.02702 0.01351 0.00677(ppi) In-vessel device PPI 37.01 74.04 147.72 In-vessel device braidedclosed 0.00024814 0.00006203 0.00001551 area (in2) In-vessel deviceBraided Open 0.00058741 0.00014680 0.00003681 Area (in2) In-vesseldevice coverage 29.7% 29.7% 29.64% In-vessel device total area (in2)0.00083555 0.00020883 0.00005232 In-vessel device cell size (mm) 1.3170.658 0.329

The occluding device may be placed into a protective coil to enhanceplacement of the occluding device in a vessel. Also, the occludingdevice may be housed in a delivery device, such as a catheter, forplacement within a vessel. The occluding device may be created at a sizeor dimension based on the size of the protective coil, delivery device,or catheter housing the occluding device. For example, the number ofstrands or ribbons in the lattice structure of the occluding device thatfit into a corresponding protective coil, delivery device, or cathetermay be determined such that the occluding device is effectively storedor housed prior to deployment in a vessel. In one example, the strandsof the occluding device may overlap in a 2-layer structure including aninner layer and an outer layer, the outer layer contacting theprotective coil.

In one example, a housing such as a protective coil, delivery device orcatheter that houses the occluding device may have a constant size ordiameter and the characteristics of the occluding device may bedetermined to fit the housing. For example, a ribbon size or width maybe determined based on the desired size of the housing. In this way, thesize (or diameter) of the housing (e.g., protective coil, deliverydevice or catheter) may be constant for a variety of occluding devicesthat may vary in size or number of ribbons.

FIG. 21 illustrates an example of a cross sectional view of a protectivecoil. In this example, a number of strands or ribbons in a latticestructure of an occluding device is determined for a protective coil.The protective coil illustrated in FIG. 21 has a circular crosssectional area with a diameter. A strand or ribbon of a predeterminedthickness or size is placed within the protective coil such that theouter surface of the strand/ribbon contact the inner surface of theprotective coil. The inner surface of the strand/ribbon creates aconcave surface within the protective coil. A second strand/ribbon isplaced within the protective coil such that the outer surface of thesecond strand/ribbon contacts an inner circumference in contact with thethe concave surface of the strand/ribbon previously placed in theprotective coil. The angle from a center point of the circularprotective coil from one edge of the second strand/ribbon to an oppositeedge of the second strand/ribbon is determined (i.e., the “arc-angle”).Based on these measurements, the number of strands or ribbons of thepredetermined size or thickness may be determined as follows:(Arc-angle)*(# ribbons/2)<=360 degrees (i.e., # ribbons<=720degrees/angle).

In the example illustrated in FIG. 21, an occluding device isconstructed using a 0.001 by 0.004 inch ribbon. The arc-angle of theribbon element at the center of the protective coil between a first linedrawn from the center point of the protective coil to one edge of aninner layer ribbon and a second line drawn from the center point of theprotective coil to the opposite edge of the inner layer ribbon is 34.14degrees. Thus, the calculated number of ribbons is less than or equal to720 degrees/34.14 degrees=20 ribbons.

TABLE 2 illustrates additional examples of different designs for loadinga lattice structure of an occluding device in a protective coil. TABLE 2# ribbons 16 32 64 Protective Coil ID (in) 0.017 0.017 0.017 RibbonWidth (in) 0.004 0.002 0.001 Ribbon Thickness (in) 0.001 0.001 0.001Inner Circle Angle 36.98 17.83 8.84 Max # Ribbons fitting in innercircle 9.73 20.19 40.72 # ribbons in inner circle 8 16 32

FIG. 22 illustrates another example of determining ribbon dimensions foran occluding device in a protective coil or a delivery device. In thisexample, an occluding device with a lattice or braid structure based ona thickness of a ribbon. As FIG. 22 illustrates, the diameter of theprotective coil or delivery device 2301 is 0.0170 inches. A first ribbon2302 is fitted within the outer surface of the protective coil ordelivery device 2301. A second ribbon 2303 is placed in contact with aninner circumference of the protective coil or delivery device 2301 wherethe inner circumference is a circumference that is tangential to theinner surface of the first ribbon 2302. The second ribbon 2303 is placedwithin the inner circumference such that lateral ends of the secondribbon 2303 are in contact with the inner circumference of theprotective coil or delivery device 2301. The arc-angle between a firstline extending from the center point of the protective coil or deliverydevice 2301 to one lateral end of the second ribbon 2303 and a secondline extending from the center point of the protective coil or deliverydevice 2301 to the other lateral end of the second ribbon 2303 iscalculated as illustrated in FIG. 22.

In this example, the maximum dimensions of the first and second ribbons2302, 2303 are determined based on the calculated arc-angle formed. Forexample, to allow eight ribbons in the inner circumference of theprotective coil or delivery device 2301, the arc-angle may be calculatedas (360 degrees)/8=45 degrees as FIG. 22 illustrates. Based on a 45degree angle, the maximum ribbon width may be determined as 0.00476inches to allow eight ribbons of a thickness of 0.001 inches to fitwithin the inner circumference of the protective coil or delivery device2301.

In another example, a narrower ribbon width is used to compensate formaterial tolerance variations and curvature. Based on extensive researchand experimentation by the applicants, it was discovered that atolerance range applied to the ribbon widths of about 20% can compensatefor such material tolerance variations. FIG. 23 illustrates an exampleof a 20% tolerance range or cushion applied to ribbon widths of anoccluding device.

In this example, 20% additional ribbons are desired in the occludingdevice (i.e., 1.20*8=9.6 ribbons). The maximum width of the ribbons maybe determined based on the desired number of 9.6 ribbons by calculatingthe angle as described above. Specifically, the arc-angle may becalculated as (360 degrees)/9.6=37.7 degrees. Based on this calculation,the maximum width of the ribbons may be determined as 0.00405 inches asillustrated in FIG. 23. Thus, in this example, a 20% cushion is appliedto permit 9.6 ribbons in the protective coil or delivery device at amaximum width of 0.00405 inches.

Table 3 provides additional examples of ribbon widths for various ribbonthicknesses. In the examples provided in Table 3, the ribbon thicknessesrange from 0.0007 inches to 0.0015 inches. TABLE 3 Ribbon Thickness (in)Calculated max width (in) 20% cushion width (in) 0.0005 0.0054300.000463 0.0006 0.00530 0.00452 0.0007 0.00516 0.00440 0.0008 0.005030.00428 0.0009 0.00490 0.00417 0.0010 0.00476 0.00405 0.0011 0.004630.00393 0.0012 0.00450 0.00382 0.0013 0.00436 0.00370 0.0014 0.004220.00358 0.0015 0.00409 0.00346

In another example, an occluding device containing 32 ribbons isdescribed. FIG. 24 illustrates an example of determining the ribbonwidth of a 32-ribbon occluding device based on the number of ribbonsthat can fit in the protective coil or delivery device 2501. In thisexample, the protective coil or delivery device 2501 has a diameter of0.017 inches and the maximum ribbon width that can fit in the innercircumference of the protective coil or delivery device 2501 provides anarc-angle of (360 degrees)/(32/2)=22.5 degrees as illustrated in FIG.24. Hence, to fit 16 ribbons along the inner circumference of theprotective coil 2501, the width of the ribbons is determined to be0.00266 inches, with a thickness of 0.00080 inches as illustrated inFIG. 24. Similarly a 20% cushion may be applied to the ribbon widts toprovide for narrower ribbon widths to compensate for material tolerancevariations. In this example, the modified ribbon widths may bedetermined based on the new arc-angle requirement of (360degrees)/19.2=18.75 degrees. Table 4 provides maxiumum ribbon widths fora 32-ribbon occluding device. TABLE 4 Ribbon Thickness (in) Calculatedmax width (in) 20% cushion width (in) 0.0005 0.00288 0.00242 0.00060.00281 0.00235 0.0007 0.00273 0.00229 0.0008 0.00266 0.00223 0.00090.00258 0.00216 0.0010 0.00251 0.00210

Alternatively, a larger number of ribbons may be included in theoccluding device. For example, the strands or ribbons may be increasedto greater than 32, such as 40, 44, 48, 50, 56, 60, 64, 70, 76, 80, 90,100, or more. For any desired number of ribbons, a ribbon width may bedetermined based on a calculated angle or a ribbon thickness asdescribed. In addition, a cushion may be applied to the ribbon width asdescribed.

In another example, oversized occluding devices may be used relative tothe vessel. For example, a larger occluding device relative to the sizeof the vessel lumen may result in enhanced anchoring of the occludingdevice within the lumen of the vessel. FIG. 25 illustrates arelationship between the PPI of the occluding device in place in thevessel (“in-vessel PPI”) versus the PPI of the occluding device in thefree-standing state (“braided PPI”). The graph in FIG. 25 demonstratesthat for each design, the PPI of the occluding device in place in thevessel approaches a maximum value as the pick count of the occludingdevice in the free-standing state increases. For example, for the 4 mmvessel design, as the PPI of the free-standing occluding device isincreased, the PPI of the occluding device in the vessel increases untilthe in-vessel PPI reaches about 45. When the in-vessel PPI reaches about45, further increases in the braided PPI result in only minimal furtherincreases in the in-vessel PPI. Also illustrated in FIG. 25, differentvessel designs (e.g., 3 mm vessel design or 5 mm vessel design) resultin a similar behavior in which the in-vessel PPI approaches a maximumvalue for high braided pick counts.

Similarly, FIG. 28 illustrates the in-vessel PPI as a function of thebraided PPI of a 32 ribbon occluding device. In the examples illustratedin FIG. 28, the PPI of the occluding device in a vessel (“in-vesselPPI”) approaches a maximum value as the PPI of the occluding device in afree-standing state (“braided PPI”). FIG. 28 also illustrates alternatevessel designs. As can be seen in the examples of vessel designs of FIG.28, for each of the vessel designs, the in-vessel PPI approaches amaximum value asymptotically as the braided PPI increases.

Similarly, the coverage of the occluding device may be based on ribbonwidth or braided PPI. FIG. 26 illustrates an example in which the ribbonis 0.00467 inches wide and 0.001 inches and is the maximum ribbon sizethat fits in the protective coil. As FIG. 26 illustrates, the coverageapproaches a maximum value of approximately 65-100 PPI range. In thisexample, the percentage of coverage asymptotically approachesapproximately 40% for a 0.001″×0.00467″ ribbon and 34% for a0.001″×0.004″ ribbon.

FIG. 29 illustrates the percent coverage as a function of the braidedPPI for a 32 ribbon occluding device. As FIG. 29 demonstrates, the %coverage approaches a maximum value as the braided PPI in increases. Forexample, for an occluding device containing 0.0008×0.00266 inch ribbons,the % coverage approaches a maximum value of about 43% as the braidedPPI increases above about 150. Also, for an occluding device containing0.0008×0.0020 inch ribbons, the % coverage approaches a maximum value ofabout 35% as the braided PPI increases above about 150.

FIG. 27 is a graph showing the opening sizes of braiding elements in theoccluding device as a function of the PPI of the lattice structure. Asthe PPI increases, the opening sizes or spaces through which flow offluid (e.g., blood) decreases. As the PPI of the lattice structurereaches about 100, the opening sizes of the braiding elements when inplace in a vessel asymptotically approaches a minimum value. In theexamples illustrated in FIG. 27, for a ribbon size of 0.001×0.004inches, the opening sizes of the braiding elements in the latticestructure of an occluding device in a vessel approaches 1280 microns orless. Similarly, for a ribbon size of 0.001×0.00467 inches, the openingsizes of the braiding elements in the lattice structure of an occludingdevice in a vessel approaches about 1220.

FIG. 30 illustrates the opening sizes of braiding elements in theoccluding device as a function of the braided PPI of the latticestructure for a 32 ribbon occluding device. As FIG. 30 demonstrates, theopening size of braiding elements approaches a minimum value as thebraided PPI in increases. For example, for an occluding devicecontaining 0.0008×0.00266 inch ribbons, the opening size approaches aminimum value of about less than 600 microns as the braided PPIincreases above about 150. Also, for an occluding device containing0.0008×0.0020 inch ribbons, the opening sizes approaches a minimum valueof about 640 as the braided PPI increases above about 150.

The occluding device 30 is radially compressible and radially expandablewithout the need for supplemental radially expanding force, such as aninflatable balloon. The occluding device 30 is constructed by windingthe two strands (31, 32 in opposite directions. Alternatively, greaterthan 2 strands may be wound in various directions. For example, 8, 10,12, 14, 22, 28, 30, 32, 36, 40, 44, 48, 52, 58, 64, 70, 86, 90, 110,116, 120, 128, 136, 150, or greater strands may be wound in variousdirections. In an embodiment, the strands 31, 32 are in the shape ofrectangular ribbon (See FIG. 4C). The ribbons can be formed of knownflexible materials including shape memory materials, such as Nitinol,platinum and stainless steel.

The ribbon used as the braiding material for the strands 31, 32 caninclude a rectangular cross section 35 (FIG. 4C). As shown in FIGS. 4Cand 7, the surface 36 that engages an inner surface of the vessel has alonger dimension (width) when compared to the wall 38 that extendsbetween the surfaces 36, 37 (thickness). A ribbon with rectangular crosssection has a higher recovery (expansive) force for the same wallthickness when compared to a wire with a circular (round) cross section.Additionally, a flat ribbon allows for more compact compression of theoccluding device 20 and causes less trauma to the vascular wall whendeployed because it distributes the radial expansion forces over agreater surface area. Similarly, flat ribbons form a more flexibledevice for a given lattice density because their surface area (width) isgreater for a given thickness in comparison to round wire devices.

While the illustrated embodiment discloses a ribbon having a rectangularcross section in which the length is greater than its thickness, theribbon for an alternative embodiment of the disclosed occluding devicesmay include a square cross section. In another alternative embodiment, afirst portion of the ribbon may include a first form of rectangularcross section and a second portion 39 of the ribbon (FIG. 4B) mayinclude a round, elliptical, oval or alternative form of rectangularcross section. For example, end sections of the ribbons may havesubstantially circular or oval cross section and the middle section ofthe ribbons could have a rectangular cross section.

In an alternative embodiment as described above, the occluding device 30can be formed by winding more than two strands of ribbon. In anembodiment, the occluding device 30 could include as many as sixteenstrands of ribbon. In another embodiment, the occluding device 30 caninclude as many as 32 strands of ribbon, as many as 48 strands ofribbon, as many as 60 strands of ribbon, as many as 80 strands ofribbon, as many as 100 strands of ribbon, as many as 150 strands ofribbon or greater than 150 strands of ribbon, for example. By usingstandard techniques employed in making radially expanding stents, onecan create an occluding device 30 with interstices 34 that are largerthan the thickness of the ribbon or diameter of the wire. The ribbonscan have different widths. In such an embodiment, the differentribbon(s) can have different width(s) to provide structure support tothe occluding device 30 and the vessel wall. The ribbons according tothe disclosed embodiments can also be formed of different materials. Forexample, one or more of the ribbons can be formed of a biocompatiblemetal material, such as those disclosed herein, and one or more of theribbons can be formed of a biocompatible polymer.

FIG. 5 shows the intravascular occluding device 30 in a radiallycompressed state located inside the micro-catheter 25. In oneembodiment, the occluding device 30 could be physically attached to thecatheter tip. This could be accomplished by constraining the occludingdevice 30 in the distal segment of the micro-catheter. Themicro-catheter 25 is slowly advanced over a guidewire (not shown) by aplunger 50 and when the tip of the micro-catheter 25 reaches theaneurysm, the occluding device is released from the tip. The occludingdevice 30 expands to the size of the vessel and the surface of theoccluding device 30 is now apposed to the vessel wall 15 as shown inFIG. 6. Instruments and methods for delivering and deploying theoccluding device 30 are disclosed in the above-referenced copendingapplication.

With reference to FIG. 7, the occluding device 30 is deployed inside thelumen of a cerebral vessel 13 with an aneurysm 10. During itsdeployment, the proximal end 43 of the occluding device 30 is securelypositioned against the lumen wall of the vessel 13 before thebifurcation 15 and the distal end 45 of the occluding device 30 issecurely positioned against the lumen wall of the vessel 13 beyond theneck 11 of aneurysm 10. After the occluding device 30 is properlypositioned at the desired location within the vessel 13 (for example,see FIG. 7), flow inside the lumen of aneurysm 10 is significantlyminimized while the axial flow within the vessel 13 is not significantlycompromised, in part due to the minimal thickness of the walls 38.

The flow into the aneurysm 10 will be controlled by the lattice densityof the ribbons and the resulting surface coverage. Areas having greaterlattice densities will have reduced radial (lateral) flow. Conversely,areas of lesser lattice densities will allow significant radial flowthrough the occluding device 30. As discussed below, the occludingdevice 30 can have longitudinally extending (lateral) areas of differentdensities. In each of these areas, their circumferential densities canbe constant or vary. This provides different levels of flow throughadjacent lateral areas. The location within a vessel of the areas withgreater densities can be identified radiographically so that therelative position of the occluding device 30 to the aneurysm 10 and anyvascular branches 15, 16 can be determined. The occluding device 30 canalso include radiopaque markers.

The reduction of blood flow within the aneurysm 10 results in areduction in force against the wall 14 and a corresponding reduction inthe risk of vascular rupturing. When the force and volume of bloodentering the aneurysm 10 is reduced by the occluding device, the laminarflow into the aneurysm 10 is stopped and the blood within the aneurysmbegins to stagnate. Stagnation of blood, as opposed to continuous flowthrough the lumen 12 of the aneurysm 10, results in thrombosis in theaneurysm 10. This also protects the aneurysm from rupturing.Additionally, due to the density of the portion of the occluding device30 at the bifurcation 15, the openings (interstices) 34 in the occludingdevice 30 allow blood flow to continue to the bifurcation 15 and theside branches 16 of the vessel. If the bifurcation 15 is downstream ofthe aneurysm, as shown in FIG. 8, the presence of the occluding device30 still channels the blood away from the aneurysm 10 and into thebifurcation 15.

The occluding devices described herein have flexibility to conform tothe curvature of the vasculature. This is in contrast to coronary stentsthat cause the vasculature to conform essentially to their shape. Theability to conform to the shape of the vasculature is more significantfor neurovascular occluding devices than coronary stents, as thevasculature in the brain is smaller and more tortuous. Tables 5 and 6demonstrate these characteristics of the claimed neurovascular occludingdevice. To demonstrate that the disclosed occluding devices exhibit verydesirable bending characteristics, the following experiment wasperformed. The occluding device made by the inventors was set on asupport surface 90 as shown in FIG. 9. About 0.5 inches of the occludingdevice 30 was left unsupported. Then, a measured amount of force wasapplied to the unsupported tip until the occluding device was deflectedby 90 degrees from the starting point. A similar length of acommercially available coronary stent was subjected to the same bendingmoment. The results are shown in Table 5. Similar to the reducedcompressive force, the occluding device of the present inventionrequired an order of magnitude lower bending moment (0.005 lb-incompared to 0.05 lb-in for a coronary stent). TABLE 5 Bending ForceRequired to Bend a 0.5″ Cantilever Made by the Occlusion Device Coronarystent commercially available stent 0.05 lb-in Neurovascular OccludingDevice (30) 0.005 lb-in

The occluding devices according to the present invention also providesenhanced compressibility (i.e., for a given force how much compressioncould be achieved or to achieve a desired compression how much forceshould be exerted) compared to coronary stents. An intravascular devicethat is not highly compressible is going to exert more force on thevessel wall compared to a highly compressible device. This is ofsignificant clinical impact in the cerebral vasculature as it isdetrimental to have an intravascular device that has lowcompressibility. TABLE 6 Compressive Force Required to Compress theOccluding device to 50% of the Original Diameter (see FIG. 10) Coronarystem (commercially available  0.2 lb Neurovascular Occluding device (30)0.02 lb

FIGS. 11-13 show an embodiment of the occluding device 60 in which thelattice structure 63 of the occluding device 60 is non-uniform acrossthe length of the occluding device 60. In the mid-section 65 of theoccluding device 60, which is the section likely to be deployed at theneck of the aneurysm, the lattice density 63 a is intentionallyincreased to a value significantly higher than the lattice densityelsewhere in the occluding device 60. For example, as seen in FIG. 11,lattice density 63A is significantly higher than the lattice density 63in adjacent section 64. At one extreme, the lattice density (porosityprovided by the interstices) could be zero, i.e., the occluding device60 is completely impermeable. In another embodiment, the lattice density63A in mid-section 65 could be about 50%, while the lattice density inthe other sections 64 of the occluding device is about 25%. FIG. 12shows such an occluding device 60 in a curved configuration and FIG. 13shows this occluding device 60 deployed in the lumen of a vessel. FIG.13 also illustrates the part of the occluding device 60 with increasedlattice density 63A positioned along the neck of aneurysm 10. As withany of the disclosed occluding devices, the lattice density of at leastone portion of occluding device 60 can be between about 20% and about80%. The lattice density of these embodiments could be between about 25%and about 50%.

Another embodiment of the occluding device 300 is shown in FIGS. 14 and15. In this embodiment, the occluding device 300 is deployed in lumen ofa vessel with an aneurysm. The occluding device 300 includes a surface310 that faces the lumen of the aneurysm. This surface 310 has asignificantly higher lattice density (smaller and/or fewer interstices)compared to the diametrically opposite surface 320. Due to the higherlattice density of surface 310, less blood flows into the lumen of theaneurysm. However, there is no negative impact on the blood flow to theside branches as the lattice density of the surface 320 facing the sidebranches is not reduced.

Any of the occluding devices disclosed herein can be used with a secondoccluding device to create a bifurcated occluding device 400 as shown inFIG. 16. This device could be created in vivo. In forming the occludingdevice 400, a portion of a first occluding device 410 having a lowdensity can be combined with a portion of a second occluding device 410that also has a low density. The occluding devices 410, 420 can be anyof those discussed herein. After these portions of the two occludingdevices 410, 420 are combined in an interwoven fashion to form aninterwoven region 425, the remaining portions 414, 424 can branch off indifferent directions, thereby extending along two braches of thebifurcation. Areas outside of the interwoven region 425 can have greaterlattice density for treating an aneurysm or lesser lattice density forallowing flow to branches 15, 16 of the vessel.

The density of the lattice for each of the disclosed occluding devicescan be about 20% to about 80% of the surface area of its occludingdevice. In an embodiment, the lattice density can be about 20% to about50% of the surface area of its occluding device. In yet anotherembodiment, the lattice density can be about 20% to about 305 of thesurface area of its occluding device.

A typical occluding device having sixteen strand braids with 0.005 inchwide ribbon, 30 picks per inch (PPI) (number of crosses/points ofcontact per inch), and 0.09 inch outer diameter has approximately 30% oflattice density (surface covered by the ribbon). In the embodimentsdisclosed herein, the ribbon can be about 0.001 inch thick with a widthof between about 0.002 inch to about 0.005 inch. In an embodiment, theribbon has a thickness of about 0.004 inch. For a 16-strands ribbon thatis about 0.001 inch thick and about 0.004 inch wide, the coverage for 50PPI, 40 PPI, and 30 PPI will have 40%, 32% and 24% approximate surfacecoverage, respectively. For a 16-strands ribbon that is about 0.001 inchthick and about 0.005 inch wide, the coverage for 50 PPI, 40 PPI, and 30PPI will be about 50%, 40% and 30% approximate surface coverage,respectively.

In choosing a size for the ribbon, one must consider that, when theribbons are bundled up, will they traverse through a micro-catheter. Forexample, sixteen strands of a 0.006 inch wide ribbon may not passthrough a micro-catheter having an internal diameter of 0.027 inch orless. However, as the width of ribbons become smaller, the recoverystrength may decrease proportionally.

While other strand geometry may be used, these other geometries, such asround, will limit the device due to their thickness dimension. Forexample, a round wire with a 0.002 inch diameter will occupy up to 0.008inch in cross sectional space within the vessel. This space can impactand disrupt the blood flow through the vessel. The flow in the vesselcan be disrupted with this change in diameter.

Although the detailed description contains many specifics, these shouldnot be construed as limiting the scope of the invention but merely asillustrating different examples and aspects of the invention. It shouldbe appreciated that the scope of the invention includes otherembodiments not discussed in detail above. Various other modifications,changes and variations which will be apparent to those skilled in theart may be made in the arrangement, operation and details of the methodand apparatus of the present invention disclosed herein withoutdeparting from the spirit and scope of the invention as defined in theappended claims. Therefore, the scope of the invention should bedetermined by the appended claims and their legal equivalents.Furthermore, no element, component or method step is intended to bededicated to the public regardless of whether the element, component ormethod step is explicitly recited in the claims.

In the claims, reference to an element in the singular is not intendedto mean “one and only one” unless explicitly stated, but rather is meantto mean “one or more.” In addition, it is not necessary for a device ormethod to address every problem that is solvable by differentembodiments of the invention in order to be encompassed by the claims.

1. A tubular-shaped device for positioning within a blood vessel forembolization of an aneurysm, the device including a plurality of strandsof helically-wound material in a lattice structure forming a pluralityof braiding elements, wherein a width of a braiding element is based onthe number of strands of helically-wound material.
 2. The device ofclaim 1 wherein the width of the braiding element is proportional to aconstant.
 3. The device of claim 2 wherein the constant is equal to π.4. The device of claim 1, wherein the width of the braiding element isabout equal to [(π)*(a diameter of a forming device)]/(number of strandsof helically-wound material/2).
 5. The device of claim 1, wherein thebraiding elements contain at least two sides forming a ribbon angle, theribbon angle based on the width of the braiding element.
 6. The deviceof claim 5 wherein the ribbon angle is selectively configured based on apredetermined width of the braiding element.
 7. The device of claim 5wherein the ribbon angle is further configured for fitting the device ina vessel of a predetermined diameter.
 8. The device of claim 7 wherein asize of the ribbon angle is directly proportional to a size of the widthof the braiding element.
 9. The device of claim 1 further including aprotective coil encompassing the device.
 10. The device of claim 9wherein the number of strands of helically wound material is based onthe protective coil encompassing the device.
 11. The device of claim 10wherein the number of strands of helically wound material is about equalto or less than (720 degrees)/(Arc-angle), wherein the arc-angle isdefined by an angle at a center point of the protective coil formed bythe width of the braiding element at a peripheral surface of theprotective coil.
 12. A method for manufacturing a device in a circularcoil for positioning within a blood vessel for embolization of ananeurysm, the device including a plurality of interlacing ribbons, themethod comprising the steps of: positioning a ribbon in the coil;providing a plurality of ribbons for the device based on a calculatedarc-angle of said positioned ribbon; interlacing said ribbons to formthe device.
 13. The method of claim 12 wherein the step of positioningthe ribbon in the coil comprises: placing a first ribbon in contact withan inner surface of the coil; determining an inner circumference tangentto a bottom surface of the first ribbon; positioning a second ribbon incontact with the inner circumference, wherein the step of calculatingthe arc-angle is based on the second ribbon.
 14. The method of claim 13wherein the arc-angle is defined by an angle at a center point of theprotective coil formed by the width of the second ribbon.
 15. The methodof claim 12 wherein the plurality of ribbons is greater than or equal to8.
 16. The method of claim 15 wherein the plurality of ribbons isgreater than or equal to
 32. 17. The method of claim 16 wherein theplurality of ribbons is
 48. 18. The method of claim 16 wherein theplurality of ribbons is
 60. 19. The method of claim 16 wherein theplurality of ribbons is greater than 60.